Deprecate autotools
Require autotools users to use --enable-autotools
. This breaks the build by default, so that we can inform people about the switch to Meson:
configure: error:
*** Autotools support will be removed after the 6.0.0 release ***
Please, try the Meson based build and report any problems you might have
with it. Instructions and references can be found in README.md.
If you still want to continue building with autotools,
use --enable-autotools configure option.
I also copied the meson build instructions from the web site to replace the autotools notes in README.